How to Fix Thunderbird Cannot Connect to Server? 9 Tested Ways

Not able to access your emails or configure your email account due to Thunderbird Cannot Connect To Server or Connection Timed Out Error? This page will explain why Thunderbird’s connection to the server failed and how you can resolve the issue using expert-verified fixes.

What is Thunderbird Connection Refused/Failed Error?

While adding a new account, Thunderbird email client tries to establish a connection with the email server via TCP (Transmission Control Protocol), whether you are configuring your account manually or using auto-configuration.

When this connection can not be established, you will receive an error like “Thunderbird cannot connect to server”, “Thunderbird connection to server failed,” or “Thunderbird server not responding.”

This further stops you from sending (if IMAP connection fails) or receiving (if SMTP connection fails) emails from that email account in Thunderbird.

Reasons Why Thunderbird Failed to Connect to the Mail Server?

Users can configure almost any IMAP or POP account in Mozilla Thunderbird. However, users often get the error Thunderbird cannot connect to the server due to the following issues:

• Unstable Internet Connection: The request cannot be sent to the server without an internet connection.
• Incorrect Server Details/Settings: Thudederbird connects to the email via details like Server Name, Port No., Security Settings, etc. If incorrect, Thunderbird’s connection to the server fails as they are misdirected to the wrong IP address and not your email server.
• Add-Ons: Certain extensions may interfere with the security connection, leading to connection failure.
• DNS Resolution Issues: Due to a caching issue or an unreachable DNS server, Thunderbird may not be able to resolve the IMAP server into an accessible IP address.
• Antivirus/Firewall Blocking Connection: Antivirus & firewalls with advanced email security scanning may block connection via certain ports.
• Email Server Down: Due to technical issues on the server’s end, the server is not responding to Thunderbird.
• Change in Authentication Method: Users getting a connection to the server failed after account setup because the security method has been changed on the server’s end.
• Proxy Server Limitations: An intermediate proxy server in Thunderbird cannot connect to all IMAP/SMTP servers, and thus fails to establish a connection.

How to Fix Thunderbird Cannot Connect to Server Error?

This error can be easily resolved with the general troubleshooting fixes listed below.

Fix 1: Restart Thunderbird in Safe Mode

Launching Thunderbird in safe mode resolves the conflict caused by extensions with security/authentication processes.

1. In Thunderbird, open the Navigation menu.
2. Select Help >> Troubleshooting Mode.
3. Restart Thunderbird to connect to the server properly without error.

Fix 2: Change Your Internet Connection

Switch between the WiFi and the mobile internet, as a stable internet connection is needed to connect Thunderbird to the server.

Fix 3: Turn Off Network Proxy in Thunderbird

1. In Thunderbird, click on the Settings/Gear icon on the left.
2. Search for Network & Disk Space.
3. Under the Connections tab, click on Settings.
4. Select the No Proxy option and press OK.
   
   
5. Try to reconfigure your email account to resolve the Thunderbird cannot connect to the mail server error.

Fix 4: Verify Server Settings to Fix Thunderbird Cannot Connect to Server

If your Thunderbird server connection failed with IMAP or SMTP. Verify if you have entered the correct server details, like the incoming server name, outgoing server name, port numbers, and connection security.

If the Account is already configured, and the “Thunderbird unable to connect to server” pops up.

1. Go to the Menu in Thunderbird.
2. Select Account Settings >> Server Settings.
3. Verify details like Server Name, Connection Port, Security Protocol, Authentication method, etc.
   

Here are the general server settings to avoid the error and connect an email account in Thunderbird.

You can find the correct server details of your IMAP/POP email account in the hosting control panel if you have a custom domain or on the official website of your email service provider.

Fix 5: Temporarily Disable Firewall/Antivirus

1. Click on the Start.
2. Search for Windows Defender Firewall.
3. Click on the Turn Windows Defender Firewall on or off Option.
   
4. Select the Turn off Windows Defender Firewall and press OK to fix the Thunderbird connection to the server failed issue.
   

Fix 6: Remove the Email Account from Thunderbird and re-add it with modern OAuth or a new password.

Fix 7: Check Email Provider Server Status

If you are getting “Thunderbird could not connect to the server, connection was refused,” verify if the email server is currently down via the official source or monitoring websites such as Downdetector. 

Try to re-add the account once the server is live again. Generally, it is a temporary issue on the server’s end and is often resolved on its own in a couple of hours.

Fix 8: Disable VPN temporarily and restart Thunderbird.

Fix 9: Clear DNS Cache to Fix Thunderbird Cannot Connect to Server

1. Open Command Prompt on Windows.
2. Type in ipconfig /flushdns.
3. Restart Thunderbird upon getting the “Successfully flushed the DNS Resolver Cache” message.